In recent years, while the resolution of balances has increased, their weighing capacities have reached several kilograms to several hundred kilograms, and their use conditions have become more severe for weight sensors required to have high sensitivity. In addition, there are many cases where users use balances without regard to their weighing capacities, and due to such a difference between requirements for balances and users' awareness, balances are often subjected to unexpected overloads in many cases.
On the other hand, in some balances, for the purpose of protection of a weight sensor from overloads, an overload prevention mechanism is added. For example, in Patent Literature 1, an overload prevention mechanism is added which is configured so that a spring member 24 to support a weight sensor 12 is interposed between a fixing frame 12b of the weight sensor and an upper case 14 of a balance, the weight sensor 12 is pressed against the upper case 14 in advance with a force of a weighing capacity+α of a resilient force of the spring member 24, and when a certain plate load (overload) or more is generated, the spring member 24 resiliently deforms and causes the weight sensor 12 to separate from the upper case 14 and float and thereby be released from the overload.